LM79 NSC [National Semiconductor], LM79 Datasheet - Page 14

• Manufacturer Part Number: LM79
• Description: Microprocessor System Hardware Monitor
• Manufacturer: NSC [National Semiconductor]

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Functional Description
2.1 Internal Registers of the LM79
A typical communication with the LM79 would consist
of:
1. Write to Port x5h the LM79 Internal Address (from col-
2. Read or write the corresponding registers data with
The LM79 Internal Address latches, and does not have to be
written if it is already pointing at the desired register. The
LM79 Internal Address Register is read/write (Bit 7 is read
only).
Configuration Register
Interrupt Status Register 1
Interrupt Status Register 2
SMI Mask Register 1
SMI Mask Register 2
NMI Mask Register 1
NMI Mask Register 2
VID/Fan Divisor Register
Serial Bus Address Register
Chip Reset/VID4/Device
ID Register
POST RAM
Value RAM
Value RAM
umn 2 above) of the desired register. Alternatively, when
both ISA and Serial Bus interfaces are used, the first
step in a communication may be to read Port x5h to
ascertain the state of the Busy bit to avoid contention
with an Serial Bus communication.
reads/writes from Port x6h.
Register
TABLE 1. The internal registers and their corresponding internal LM79 address is as follows:
(This is the data to be
written to Port x5h)
LM79 Internal Hex
(Continued)
Address
00h-1Fh
20h-3Fh
60h-7Fh
40h
41h
42h
43h
44h
45h
46h
47h
48h
49h
0101 XXXX
0000 1000
0000 0000
0000 0000
0000 0000
0000 0000
0000 0000
0100 0000
0010 1101
1100 000X
Power on
14
Value
Auto-increment to the address of Interrupt Status
Register 2 after a read or write to Port x6h.
Auto-increment to the address of SMI Mask
Register 2 after a read or write to Port x6h.
Auto-increment to the address of NMI Mask
Register 2 after a read or write to Port x6h.
The first four bits set the divisor for Fan
Counters 1 and 2. The lower four bits reflect the
state of the VID0-VID3 inputs.
D7 identifies this device as the LM79. D0 reflects
the state of VID4.
Auto-increment when written to from Port x0h or
x4h. Auto-increment after a read or write to Port
x6h, with a separate pointer. Auto-incrementing
stops when address 1Fh is reached.
Auto-increment after a read or write to Port x6h.
Auto-incrementing stops when address 7Fh is
reached.
Notes